Definition and Details of Threaded Fittings ASME B16.11

Threaded Fittings general

Threaded joints probably represent the oldest method of joining piping systems. Like Socket Weld fittings, threaded fittings are mainly used for small pipe diameters (Small Bore Piping); generally for piping whose nominal diameter is NPS 2 or smaller.
The dimensional standards for taper pipe threads are given in ASME B1.20.1. That document gives all required dimensions including number of threads per inch, pitch diameter, and normal engagement lengths for all pipe diameters.

NPT Thread

All fittings on this page are described, are provided with NPT thread, ASME B1.20.1. The American National Pipe Thread Tapered, is the best known and most widely used connection where the pipe thread provides both the mechanical joint and the hydraulic seal. NPT has a tapered male and female thread which seals with Teflon® tape or jointing compound.

Dimensions of American Taper Pipe Thread, with Sealant Compound

DN-NPT Major Diameter
mm
Tapping
Drill Size mm
TPI Pitch
mm
1/16" 7.895 6.00 27 0.941
1/8" 10.242 8.25 27 0.941
1/4" 13.616 10.70 18 1.411
3/8" 17.055 14.10 18 1.411
1/2" 21.223 17.40 14 1.814
3/4" 26.568 22.60 14 1.814
1" 33.228 28.50 11.5 2.209
1.1/4" 41.985 37.00 11.5 2.209
1.1/2" 48.054 43.50 11.5 2.209
2" 60.092 55.00 11.5 2.209
2.1/2" 72.699 65.50 8 3.175
3" 88.608 81.50 8 3.175
3.1/2" 101.316 94.30 8 3.175
4" 113.973 107.00 8 3.175
5" 141.300 134.384 8 3.175
6" 168.275 161.191 8 3.175
8" 219.075 211.673 8 3.175
10" 273.050 265.311 8 3.175
12" 323.850 315.793 8 3.175
 
NPT Thread

Types of Threaded Fittings by Class and Size

Description Class Designation
2000 3000 6000
Elbows 45 and 90 degrees
Tees, Crosses, Coupling
Half-Coupling, Cap
1/2 - 4 1/2 - 2 1/2 - 2
1/2 - 4 1/2 - 2 1/2 - 2
1/2 - 4 1/2 - 2 1/2 - 2
Pipe Wall SCH 80 and XS SCH 160 XXS

Plugs and Bushings are not identified. They may be used up through Class 6000 NPS

Fittings for Threaded Pipe systems

Threaded Elbow 90 degrees Elbow 90°
This Elbows make 90° changes of direction in the run of pipe.
Threaded Tee Tee
This Tee makes 90° branch from the main run of pipe.
Threaded Cross Cross
Crosses makes 90° branch from the main run of pipe.
Threaded Elbow 45 degrees Elbow 45°
This Elbows make 45° changes of direction in the run of pipe.
Threaded Full Coupling Full-coupling
A Full Coupling, joins pipe two pipe or to a nipple etc..
Threaded Cap (End Cap) Cap (End Cap)
Seals the threaded end of pipe.
Threaded Half Coupling Half-coupling
The Half Coupling can be directly welded to the run pipe, to make a branch connection.
Threaded Square Head Plug Square head plug
Seals the threaded end of fitting.
Threaded Hex Head Plug Hex head plug
Seals the threaded end of fitting.
Threaded Round Head Plug Round head plug
Seals the threaded end of fitting.
Threaded Hex head bushing Hex head bushing
Can be used to reduce a threaded fitting.
Threaded Union Union (MSS SP-83)
Unions are primarily used for maintenance and installation purposes. It is a screwed joint design and it consists of three interconnected pieces. Two internally threads and a centerpiece that draws the ends together when rotated.

Advantages and Disadvantages of Threaded Fittings

Advantages

Disadvantages

Remark(s) of the Author...

You knew that...?

  • At the smallest sizes, the amount of wall lost during threading actually equals approximately 55% of the original pipe wall.